That wasn't too bad. The animation was good, but could be better. Everyone has room to improve on their character movement. Until your helpin' Pixar animate Toy Story 4, anyone has room to improve. The voices were good (the few I heard), especially in terms of the audio quality. It was a bit short though. So keep it up, imrpove, work on your story, and never rush.

Why is the Joker in the Wayne Manor? Why is Batman still wearing his mask in the shower? In fact, why is he even parading as his superhero persona in this supposed Wayne Manor? Is this even Wayne Manor? Maybe this is not Wayne Manor, maybe this is some other person's home, like Vicki Vale's or someplace, and Batman is just here for that person's protection, but he needed a shower because he smelled real bad, so he decided to take one for the request of the housemate, but the Joker managed to sneak into the household, and snuck into the bathroom just to pull that prank before causing more trouble like holding the housemate hostage. Or Maybe, the supposed person who Batman is supposed to protect in the house IS the Joker, because the Joker is really good at disguising himself, and The Joker actually arranged this just so he could pull that prank. Or maybe, this is just another random DC "elseworld" where the Joker and Batman are a gay couple.

nice love the fact batman has a shower with his mask on :p
use of samples is good for audio
art was simple animation was simple and effective
altogether nice humour and presentation
your flash size is off though the white bars at the bottom and top really take away from the feel a quick edit should fix that though!

that not actually that funny.
would have been better if joker climbed into the cupboard and proceeding to remove the shower cap and start pissing over batman as the prank.... yes my humor is weird.
fairly nice artwork tho, and good sound quality.